Servo-mechanism



July 13, 1965 J. c. LEJoN 3,194,010

SERVO-MECHANISM Filed Aug. 1, 1962 lf2-f1 yvvvvvvvvvvvvv INVENTOR.'

JEAN C. LEJON FIG. 2 -BY @zg/nx ATTORNEY United States Patent() 3,194,010 SERVO-MECHANSM Jean C. Lejon, Paris, France, assigner to Societ dite Controle Bailey, a company of France Filed Aug. 1, 1962, Ser. No. 213,998 4 Claims. (Cl. 60-25) The present invention relates to a servo-mechanism in which the energy is supplied by the variation in vapor pressure of a condensable fluid which is a function of the temperature of the fluid.

According to the invention, the servo-mechanism which operates by variation in the vapor pressure of a condensable fluid consists of a vapor-tight chamber, a piston inside this chamber, some Peltier effect cooling cells in one of the compartments of the chamber located on one side of the piston, a liquid in each compartment whose saturation vapor pressure is high at ordinary temperatures, and means for varying the electric current to the cells as a function of the position of the piston.

In servo-mechanisms operated by vapor pressure, to reduce the time constant of the device, it is necessary to reduce -to a minimum any thermal exchange between the calorific mass represented by the cylinder wall and the Variable temperature source which may, for example, be located in the piston. Now, in the case where the variable temperature source is a heat source, it is necessary to maintain the entire caloriiic mass at the temperature of the heat source to avoid condensation of the liuid, and this is not compatible with the reduction of thermal exchanges between cylinder wall and piston. On the other hand, if the source of variable ternperature is a source of cold, it is a question only of the temperature of the liquid, while some of the vapor may be in the superheated state without adverse effect. It is thus possible to attempt to reduce heat transfer within the vapor rather than promoting it, and this possibility permits a substantial reduction of the time constant.

The invention will now be described in detail with reference to the attached drawings in which:

FIG. l represents a vapor pressure servo-mechanism in accordance with the invention in which the Peltier effect cooling cells are situated in the base of the cylinder;

FIG. 2 is a fragmentary view of a modification of FIG. 1 in which the Peltier effect cooling cells are located in the piston.

With reference to FIG. l, 1 designates a cylinder having a top head 2 and a bottom head consisting of Peltier effect cooling cells 3. The cylinder is vaportight .and its inner wall is covered with an insulating lining 4 which has a low coefficient of friction, such as Tefion or industrial nylon.

The cylinder head 2 has a central opening 21 through which passes a piston-rod 7 of a piston 8. A gasket 5 is fitted into the opening 21, and this opening is enclosed by a bellows 6 which is fastened on one end of the cylinder head 2 and at the other end to the pistonrod 7. The combination of the gasket 5 and 4the bellows 6 assures the absolute vapor-tightness of the inner chambers 12 and 13 of the cylinder 1.

The piston 8 is preferably made of metal and its lower face covered by a heat insulating lining 9. A gasket 10 is inserted around the periphery of the piston S. The upper face of the piston is indented by a number of small depressions 11 that are iilled with a liquid which has high saturation vapor pressures at ordinary temperatures, such as Freon or liquid butane. The quantity of liquid is so determined that there is just enough liquid to provide, at a temperature somewhat above the probable 3,194,010 Patented July 13, 1965 ICC maximum ambient temperature, the amount of vapor necessary to iill the entire volume of the upper chamber 12 when the piston 8 is at the lower extreme of its travel. This, then, will serve to limit the maximum pressure within cylinder 1. Because of the limited thermal exchange between the upper 12 and lower 13 chambers, it can be admitted as a first approximation that the temperature of the upper chamber 12 will remain equal to the ambient temperature. The prevailing pressure in the chamber 12 is therefore essentially the vapor pressure of the liquid at the ambient temperature.

In the lower chamber 13, there is likewise some liquid in an amount which is just suiiicient to iill the maximum volume of the chamber with saturated vapor when the piston is at the upper extreme of its stroke, this at some predetermined temperature sufficient to maintain the maximum pressure below a predetermined value. The prevailing pressure in the chamber 13 is substantially equal to the vapor pressure of the liquid at the temperature of the surface of the cooling elements 3. Thermal contact between the liquid and the cold part of the refrigerating elements is assured by the large surface area of the latter, and by the presence of contact fins 14 perpendicular to the surface of the elements.

Linked -to the upper end of the piston-rod 7 is the core 16 of a differential transformer 15 which delivers an alternating voltage whose amplitude is proportional to the displacement of the piston 8. This voltage is rectified in a demodulator 17 and transmitted to an amplifier 18 through a summing junction 19 into which is also introduced an operating signal voltage through terminal 19A. Depending on whether the voltage coming from the demodulator is greater or smaller than the operating signal voltage, the difference in potential is positive or negative; it is amplified by the amplifier 18, which delivers a continuous output current of variable strength, to the Peltier effect cells. When the output voltage from the rectifier bridge 17 is greater than the operating signal, for example, the liquid in contact with the cells 3 is reduced in temperature causing a reduction in vapor pressure. The lowered pressure results in a downward displacement of the piston until a state of equilibrium is established between Ithe pressure existing in compartment 12 on the one hand and the prevailing pressure in compartment 13 together with the force produced by a spring 20 on the other.

In the case of FIG. 2, Peltier effect cooling cells 33 are mounted in a piston 38. As the feed current is a single direction current, the cold face and the warm face of the cells, and therefore of the piston, are always the same ones. The thermal exchange between the warm face and heat-dissipating fins 22 obviously being of the utmost importance, the lower compartment 13 of the cylinder may be filled with a compressible substance possessing good thermal conductivity, such as metal shavings 35. Similarly to minimize thermal exchanges within the gaseous phase, a compressible material of low heat conductivity may be placed in compartment 12 of FIG. 1 and 12 of FIG. 2.

While two embodiments of the invention have been herein shown and described, it will be apparent to those skilled in the art that many changes may be made in the construction and arrangement of parts without departing from the scope of the invention as defined in the appended claims.

What is claimed is:

1. In a servo-mechanism operated by the variable pressure of a condensable liquid, in combination, a vertical vapor-tight cylinder having an insulating lining for reducing the thermal exchange between the inner and outer walls of said cylinder, said lining having a low i 3 1 coeicient of friction, a movable piston in said cylinder having a lower insulated face and an upper face indented with a plurality of indentations, said insulation reducing the thermal exchange between said lower and upper faces said piston forming lower and upper chambers within said cylinder, a poolV ofliquid in each of said chambers' producing vapor pressures acting on opposite faces ,of

said piston and means for cooling said pool ofliquidY in said lower chamber to thereby vary the vapor pressure acting upon the lower face of said piston.

2. 'In a servo-mechanism operated by the variable pressure of a condensable liquid, in combination, averti, cal vapor-tight cylinder having an insulated lining for reducing the thermal exchange between the inner and outer walls of said cylinder, said lining having fa low coefcient of friction, a movable piston in said cylinder having a'series of Peltier Effect cells imbedded therein,

said piston forming an .upper and Vlower chamber withiny said cylinder, a pool of liquid in each of said chambers producing vapor pressures V4acting on opposite faces of said piston, said pressurecontrolled by the Peltier Effect cells.

, 4 Y 3. A Vservo-mechanism 4as, set forth in claim 2 wherein saidY upper chamber is lled Vwith a compressible material ofv low heat conductivity to minimize thermal exchanges within the gaseous phase. Y

Y4. A servo-mechanism as set forth in claim 2 wherein saidlower Ychamber,A is lled with a compressible substance possessing high thermal conductivity to maximize l the thermal exchange between said piston and said heatdissipating ns.

References Cited by the Examiner UNITED STATES PATENTS JULIUS EfwEsT, Primary Examiner. 

1. IN A SERVO-MECHANISM OPERATED BY THE VARIABLE PRESSURE OF A CONDENSABLE LIQUID, IN COMBINATION, A VERTICAL VAPOR-TIGHT CYLINDER HAVING AN INSULATING LINING FOR REDUCING THE THERMAL EXCHANGE BETWEEN THE INNER AND OUTER WALLS OF SAID CYLINDER, SAID LINING HAVING A LOW COEFFICIENT OF FRICTION, A MOVABLE PISTON IN SAID CYLINDER HAVING A LOWER INSULATED FACE AND AN UPPER FACE INDENTED WITH A PLURALITY OF INDENTATIONS, SAID INSULATION REDUCING THE THERMAL EXCHANGE BETWEEN SAID LOWER AND UPPER FACES SAID PISTON FORMING LOWER AND UPPER CHAMBERS WITHIN SAID CYLINDER, A POOL OF LIQUID IN EACH OF SAID CHAMBERS PRODUCING VAPOR PRESSURES ACTING ON OPPOSITE FACES OF SAID PISTON AND MEANS FOR COOLING SAID POOL OF LIQUID IN SAID LOWER CHAMBER TO THEREBY VARY THE VAPOR PRESSURE ACTING UPON THE LOWER FACE OF SAID PISTON. 